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When do toddlers start asking why?

The CDC's milestone checklist lists “Asks “who,” “what,” “where,” or “why” questions, like “Where is mommy/daddy?”” by 3 years, along with conversations of at least two back-and-forth turns. Most children (75% or more) do these by 3 years, and many start sooner. If you're worried about your child's talking, ask your pediatrician.

Checked October 29, 2026.

What the CDC's checklists say

Milestones from the CDC's “Learn the Signs. Act Early.” checklists, word for word
ByThe CDC's milestoneMonth page
3 yearsAsks “who,” “what,” “where,” or “why” questions, like “Where is mommy/daddy?”Your child at 3 years
3 yearsTalks with you in conversation using at least two back-and-forth exchangesYour child at 3 years

Each row is from the CDC's checklist for that age (3 years), checked October 29, 2026.

What “by 3 years” means

Developmental milestones are things most children (75% or more) can do by a certain age. The CDC puts each milestone at the age by which at least 75% of children would be expected to do it, so that even one missing milestone leads to a conversation with the doctor instead of “wait and see”. So “by 3 years” isn't an average. Many children do it sooner, and the checklists don't list everything a child learns.

What it can look like

"Where's Daddy?" "What's that?" and then, many times a day, "Why?"

What helps

  • Answer simply, then ask back: "Why do you think?"
  • Ask your own questions on walks: "Where's that bus going?"
  • "I don't know, let's find out" is a good answer too.

Talk to your pediatrician if…

Your child isn't doing this by 3 years, the age on the CDC's list, has lost a skill they once had, or you're worried for any reason.

You know your child best. Don't wait. If your child is not meeting one or more milestones, has lost skills he or she once had, or you have other concerns, act early. Talk with your child's doctor, share your concerns, and ask about developmental screening.

If you or the doctor are still concerned, the CDC says to ask for a referral to a specialist, and to call your state's early intervention program (find the number on the CDC's list). You do not need to wait for a doctor's referral or a medical diagnosis to make this call. If your child is age 3 or older, call any local public elementary school (even if your child does not go to school there) and say: "I have concerns about my child's development and I would like to have my child evaluated through the school system for preschool special education services."

More from the CDC: Concerned about your child's development? If your child seems unwell, call your pediatrician, or 911 in an emergency.

Sources